Alcatel-Lucent 7450 Quality Of Service Manual page 690

Ethernet service switch; service router; extensible routing system

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Table of Contents

QoS Model for ATM-Based Services

Cell Level Per-VC Queues

Strict Priority

Non-Shaped VC 2

This section provides a description of the QoS model used for ATM-based services on the

router ATM MDA. Although slight variations of this model are applied on other ATM

capable MDAs, the principles remain the same. An example of a VPLS Service with ATM

SAP is shown in

When Ethernet frames are sent over an ATM VC, the scheduling of data becomes hierarchical

with two main levels: packet level scheduling and per-VC cell level scheduling.

At the first level, frames are queued on a per-CoS (or forwarding class), per-VC basis in order

to achieve the proper class of service differentiation for the frames in the same VC. Each

Ethernet frame is queued based on the VC dedicated forwarding class queue, as configured

in the service egress QoS policy. The packet level scheduling can make use of HQoS

scheduler policy in order to enforce aggregate bandwidth among a group of queues feeding

an ATM VC or to enforce aggregation of bandwidth across all queues of all VCs at a given

customer site.

The frame level scheduling is the same for other types of SAP (Ethernet, FR, and PPP) and

all the features available on the service ingress and egress QoS policies can be applied.

At the second level, the segmented cells are queued in per-VC queues according to the service

category of the ATM traffic descriptor profile applied to the ATM SAP. Scheduling at the

ATM level enforces the priority and bandwidth sharing desired at the cell level.

Figure 40: Hierarchical Scheduling for ATM-Based Services

Packet Level Forwarding

Class Queues

Strict Priority

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